Lateral bipolar transistor

ABSTRACT

A bipolar junction transistor comprises a semiconductor layer disposed on an insulating material, at least a portion of the semiconductor layer forming a base region. The bipolar junction transistor further comprises a transistor emitter laterally disposed on a first side of the base region, where in the transistor emitter is a first doping type and has a first width, and wherein the first width is a lithographic feature size. The bipolar junction transistor further comprises a transistor collector laterally disposed on a second side of the base region, wherein the transistor collector is the first doping type and the first width. The bipolar junction transistor further comprises a central base contact laterally disposed on the base region between the transistor emitter and the transistor collector, wherein the central base contact is a second doping type and has a second width, and wherein the second width is a sub-lithographic feature size.

FIELD OF THE INVENTION

The present invention relates generally to the fabrication ofsemiconductor devices, and more particularly to the fabrication of alateral bipolar transistor.

BACKGROUND OF THE INVENTION

A bipolar junction transistor (BJT) is a three-terminal electronicdevice constructed of doped semiconductor materials, which may be usedin amplifying or switching applications. The operation of bipolarjunction transistors includes both electrons and holes. Charge flow in aBJT is due to bidirectional diffusion of charge carriers across ajunction between two regions of different charge concentrations. Themode of operation of a BJT is contrasted with unipolar transistors, suchas field effect transistors, in which only one carrier type is involvedin charge flow due to drift. By design, most of the BJT collectorcurrent is due to the flow of charges injected from a high-concentrationemitter into the base where there are minority carriers that diffusetoward the collector.

Conventional epitaxial semiconductor growth of the doped regions of aBJT typically requires high temperatures (generally much greater than600° C.). Depending on the application, the high epitaxial growthtemperature may have any or all of the following drawbacks: degradationof minority carrier lifetime, creation of structural defects, undesiredimpurity diffusion resulting in junction widening, relaxation of strain,or generation of undesirable strain resulting in buckling ordelamination.

SUMMARY

Embodiments of the present invention include a bipolar junctiontransistor and a method of making the same. The bipolar junctiontransistor comprises a semiconductor layer disposed on an insulatingmaterial, at least a portion of the semiconductor layer forming a baseregion. The bipolar junction transistor further comprises a transistoremitter laterally disposed on a first side of the base region, where inthe transistor emitter is a first doping type and has a first width, andwherein the first width is a lithographic feature size. The bipolarjunction transistor further comprises a transistor collector laterallydisposed on a second side of the base region, wherein the transistorcollector is the first doping type and has the first width. The bipolarjunction transistor further comprises a central base contact laterallydisposed on the base region between the transistor emitter and thetransistor collector, wherein the central base contact is a seconddoping type and has a second width, and wherein the second width is asub-lithographic feature size.

The method of making the bipolar junction transistor includes providinga semiconductor layer on an insulating material, wherein thesemiconductor layer forms a base region. Next, depositing a passivationlayer on the base region. Next etching two or more openings in thepassivation layer, wherein the two or more openings have a width of alithographic feature size and expose the base region. Lastly,epitaxially growing a first doped layer in the two or more openings inthe passivation layer, wherein the first doped layer is a first dopingtype.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a pictorial representation (through a cross-sectional view)depicting a structure including a passivation layer located atop acrystalline semiconductor substrate, in accordance with an embodiment ofthe present invention;

FIG. 2 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 1 after forming at least one openingwithin the passivation layer that exposes at least one portion of thesurface of the crystalline semiconductor substrate, in accordance withan embodiment of the present invention;

FIG. 3 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 2 after growth of a n-type dopant layerin the at least one opening from the exposed portion of the surface ofthe crystalline semiconductor substrate, in accordance with anembodiment of the present invention;

FIG. 4 is a pictorial representation (through a cross-sectional view)depicting depositing of a high-k dielectric material over the structureof FIG. 3, in accordance with an embodiment of the present invention;

FIG. 5 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 4 after chemical-mechanicalplanarization to the height of the passivation layer, in accordance withan embodiment of the invention;

FIG. 6 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 5 after etching the passivation layerbetween the n-type dopant layer that exposes at least one portion of thesurface of the crystalline semiconductor substrate, in accordance withan embodiment of the invention;

FIG. 7 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 6 with a formed spacer, in accordancewith an embodiment of the present invention;

FIG. 8 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 7 after growth of a p-type dopant layerbetween the n-type dopant layer and formed spacer from the exposed atleast one portion of the surface of the crystalline semiconductorsubstrate, in accordance with an embodiment of the present invention;

FIG. 9 is a pictorial representation (through a cross-sectional view)depicting a structure including a high-k dielectric material locatedatop a crystalline semiconductor substrate, in accordance with anotherembodiment of the present invention;

FIG. 10 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 9 after forming at least one openingwithin the high-k dielectric material that exposes at least one portionof the surface of the crystalline semiconductor substrate, in accordancewith another embodiment of the present invention;

FIG. 11 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 10 after growth of a n-type dopant inthe at least one opening from the exposed portion of the surface of thecrystalline semiconductor substrate, in accordance with anotherembodiment of the present invention;

FIG. 12 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 11 after thermal oxidation of theexposed n-type dopant layer including diffusion into the crystallinesemiconductor substrate, in accordance with another embodiment of thepresent invention;

FIG. 13 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 12 after etching the high-k dielectricmaterial between the n-type dopant layer that exposes at least oneportion of the surface of the crystalline semiconductor substrate, inaccordance with another embodiment of the invention;

FIG. 14 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 13 with a formed spacer, in accordancewith another embodiment of the invention;

FIG. 15 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 14 after growth of a p-type dopant layerbetween the n-type dopant layer and formed spacer from the exposed atleast one portion of the surface of the crystalline semiconductorsubstrate, in accordance with another embodiment of the presentinvention;

FIG. 16 is a pictorial representation (through a cross-sectional view)depicting a structure including a high-k dielectric material orpassivation layer located atop a crystalline semiconductor substrate, inaccordance with another embodiment of the present invention;

FIG. 17 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 16 after forming at least one openingwithin the high-k dielectric material or passivation layer that exposesat least one portion of the surface of the crystalline semiconductorsubstrate, in accordance with another embodiment of the presentinvention;

FIG. 18 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 17 after growth of a n-type dopant layerin the at least one opening from the exposed portion of the surface ofthe crystalline semiconductor substrate, in accordance with anotherembodiment of the present invention;

FIG. 19 is pictorial representation (through a cross-sectional view)depicting the structure of FIG. 18 after etching the high-k dielectricmaterial or passivation layer adjacent to the n-type dopant layers toform at least one opening that exposes at least one portion of thesurface of the crystalline semiconductor substrate, in accordance withanother embodiment of the invention;

FIG. 20 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 19 after thermal oxidation of theexposed n-type dopant layer and crystalline semiconductor substrateincluding diffusion into the crystalline semiconductor substrate, inaccordance with another embodiment of the present invention;

FIG. 21 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 20 after maskless isotropic timedetching to remove oxide on the crystalline semiconductor substrate, butleaving oxide on the n-type dopant layer, in accordance with anotherembodiment of the present invention;

FIG. 22 is a pictorial representation (through a cross-sectional view)depicting depositing of a high-k dielectric material over the structureof FIG. 21, in accordance with another embodiment of the presentinvention;

FIG. 23 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 22 after etching a portion of the high-kdielectric material on the n-type dopant layers exposing a portion ofthe thin layer of oxide on each n-type dopant layer and etching thehigh-k dielectric material between the n-type dopant layers exposing thesurface of the crystalline semiconductor substrate, in accordance withanother embodiment of the present invention;

FIG. 24 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 20 after masked isotropic time-etch toremove oxide between the n-type dopant layer that exposes at least oneportion of the surface of the crystalline semiconductor substrate, inaccordance with another embodiment of the invention; and

FIG. 25 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 24 after growth of a p-type dopant layerbetween the n-type dopant layer and oxide layer from the exposed atleast one portion of the surface of the crystalline semiconductorsubstrate, in accordance with another embodiment of the presentinvention.

DETAILED DESCRIPTION

Embodiments of the present invention generally provide a new process offorming bipolar junction transistors (BJT). Additionally, embodiments ofthe present invention provide a lateral bipolar transistor in which thebase width, w, is formed at sub-lithographic dimensions. Thelithographic feature size or smallest dimension printed is F. Withinthis invention, w is given by the formula, w=F−2*s. The spacer width iss, wherein a dielectric spacer of thickness s has been introduced.

Embodiments of the present invention realize that scaling of the lateralBJT device structure to dimensions below the feature sizes used in thelithography remains a problem. Particularly, in applications where apoly-crystalline channel material is desired instead of a singlecrystalline material, for example in a back-end-of-the-line integrateddevice, scaling has benefits to performance. Specifically, embodimentsof the present invention realize the desire to scale down the base widthto make it sufficiently smaller than the diffusion length of minoritycarriers in the poly-crystalline base. The presence of structuraldefects in poly-Si results in shorter minority carrier recombinationtimes and therefore shorter diffusion lengths in poly-crystallinematerials compared to a single-crystalline material and therefore asmall based width may be advantageous. Embodiment of the presentinvention are discussed related to an n-p-n transistor and embodimentsof the present invention can be performed in a p-n-p transistor as well,as known in the art.

Detailed description of embodiments of the claimed structures andmethods are disclosed herein; however, it is to be understood that thedisclosed embodiments are merely illustrative of the claimed structuresand methods that may be embodied in various forms. In addition, each ofthe examples given in connection with the various embodiments isintended to be illustrative, and not restrictive. Further, the figuresare not necessarily to scale, some features may be exaggerated to showdetails of particular components. Therefore, specific structural andfunctional details disclosed herein are not to be interpreted aslimiting, but merely as a representative basis for teaching one skilledin the art to variously employ the methods and structures of the presentinvention.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the disclosed structures andmethods, as oriented in the drawing figures. The terms “overlying”,“atop”, “positioned on” or “positioned atop” mean that a first element,such as a first structure, is present on a second element, such as asecond structure, wherein intervening elements, such as an interfacestructure may be present between the first element and the secondelement. The term “direct contact” means that a first element, such as afirst structure, and a second element, such as a second structure, areconnected without any intermediary conducting, insulating orsemiconductor layers at the interface of the two elements. The termnon-crystalline refers to amorphous, nano-crystalline ormicro-crystalline. The term crystalline refers to single-crystalline(i.e., mono-crystalline) or poly-crystalline (i.e., multi-crystalline).

Reference is now made to FIGS. 1-8, which illustrate a selective methodof forming a bipolar junction transistor, in accordance with anembodiment of the present invention. In the selective method, apatterned passivation layer 114 is formed on an exposed surface of acrystalline semiconductor substrate 110. Next, an n-type dopant layer118 is epitaxially grown from the exposed surfaces of the crystallinesemiconductor substrate 110. A high-k dielectric layer 120 is thendeposited conformally over the passivation layer 114.Chemical-mechanical planarization is then used to remove the high-kdielectric layer 120 to the height of the passivation layer 114. Thepassivation layers 114, between n-type dopant layers 118, are etchedforming openings 122 to expose at least one portion of the surface ofthe crystalline semiconductor substrate 110, between the 2 n-typecontacts. A spacer 124 is formed adjacent the n-type dopant layer 118 inthe exposed area, within opening 122. The spacer is formed by conformaldeposition and then anisotroic etch removal of the material, againexposing substrate 110. After surface cleaning steps, a p-type dopantlayer 126 is epitaxially grown from the exposed surface of thecrystalline semiconductor substrate 110.

All figures and embodiments described below make use of the base width,w, of the bipolar transistor, and w=F−2*s, where F is the feature sizeapplied in the lithography step, and s is the sidewall thickness of thedielectric spacer. For example, when F=20 nm, the smallest dimensionprinted, a spacer thickness of 5 nm leads to w=10 nm, measurably lessthan F, and 10 nm is not printable using present lithography. In anotherexample, when F is 10 nm, the smallest dimension printed, a spacerthickness of 2 nm leads to w=6 nm, measurably less than F, and w=6 nm issmaller than any practical lithographic dimension. As known in the art,F can have a range of values, for example 10 to 100 nm. Using thisinvention, the bipolar transistor has base width w from 2 to 98 nm, forexample, and the restriction is that w is measurably smaller than F.

Referring to FIG. 1, there is a pictorial representation (through across-sectional view) depicting a structure including a passivationlayer 114 located atop a crystalline semiconductor substrate 110, inaccordance with an embodiment of the present invention. The term“crystalline” is used herein to denote a single crystal material, amulti-crystalline material or a polycrystalline material. Typically, thecrystalline semiconductor substrate 110 is comprised of a singlecrystalline semiconductor material. The term “non-crystalline” is usedherein to denote an amorphous, nano-crystalline or micro-crystallinematerial.

In one embodiment, the crystalline semiconductor substrate 110 that canbe employed in embodiments of the present invention can be an III-Vcompound semiconductor which includes at least one element from IIIA(i.e., Group 13) of the Periodic Table of Elements and at least oneelement from Group VA (i.e., Group 15) of the Periodic Table ofElements. The range of possible formulae for suitable III-V compoundsemiconductors that can be used in the present invention is quite broadbecause these elements can form binary (two elements, e.g., gallium(III)arsenide (GaAs)), ternary (three elements, e.g., indium gallium arsenide(InGaAs)) and quaternary (four elements, e.g., aluminium gallium indiumphosphide(AlInGaP)) alloys.

In another embodiment of the present invention, the crystallinesemiconductor substrate 110 can be a semiconductor material having theformula Si_(y)Ge_(1−y) wherein y is 0≦y≦1. In some embodiments, in whichy is 1, the semiconductor substrate 110 can be comprised entirely of Si.In another embodiment, in which y is 0, the semiconductor substrate 110can be comprised entirely of Ge. In yet another embodiment and when y isother than 0 or 1, the crystalline semiconductor substrate 110 can becomprised entirely of a SiGe alloy.

The crystalline semiconductor substrate 110 can be a bulk semiconductormaterial or it can be a semiconductor-on-insulator material whichincludes, from bottom to top, a handle substrate, a buried insulatinglayer, and a top semiconductor layer which is typically crystalline andis composed of either an III-V compound semiconductor, or asemiconductor material having the formula Si_(y)Ge_(1−y) wherein y is0≦y≦1. The handle substrate can be comprised of a same or differentsemiconductor material as the top semiconductor layer, while the buriedinsulating layer may be comprised of a semiconductor oxide,semiconductor nitride, semiconductor oxynitride or a multilayered stackthereof. The semiconductor-on-insulator substrate that can be employedin some embodiments of the present invention can be formed by ionimplantation and annealing, or the semiconductor-on-insulator substratecan be formed utilizing a layered transfer process. The thickness ofeach of the layers forming the semiconductor-on-insulator substrate iswithin ranges that are typically used for fabricating semiconductorstructures.

The crystalline semiconductor substrate 110, or the top crystallinesemiconductor layer of a semiconductor-on-insulator substrate, is of afirst conductivity type which is either p-type or n-type, and the dopantconcentration may be in the range from 1×10¹⁷/cm³ to 1×10¹⁹/cm³ withinthe invention. In an embodiment, this substrate doping is from 1 to5×10¹⁸/cm³. As used herein, “p-type” refers to the addition ofimpurities to an intrinsic semiconductor that creates deficiencies ofvalence electrons (i.e., holes). In a Si-containing semiconductormaterial, examples of p-type dopants, i.e., impurities, include but arenot limited to, boron, aluminum, gallium and indium. In one embodiment,in which the first conductivity type of the semiconductor material ofthe crystalline semiconductor substrate 10 or the top crystallinesemiconductor layer of a semiconductor-on-insulator substrate is p-type,the p-type dopant is present in a concentration ranging from 1×10⁹atoms/cm³ to 1×10²⁰ atoms/cm³. In another embodiment, in which the firstconductivity type is p-type, the p-type dopant is present in aconcentration ranging from 1×10¹⁴ atoms/cm³ to 1×10¹⁹ atoms/cm³. As usedherein, “n-type” refers to the addition of impurities that contributesfree electrons to an intrinsic semiconductor. In a Si-containingsemiconductor, examples of n-type dopants, i.e., impurities, include butare not limited to, antimony, arsenic and phosphorous. In oneembodiment, in which the first conductivity type of the semiconductormaterial of the crystalline semiconductor substrate 110 or the topcrystalline semiconductor layer of a semiconductor-on-insulatorsubstrate is n-type, the n-type dopant is present in a concentrationranging from 1×10⁹ atoms/cm³ to 1×10²⁰ atoms/cm³. In another embodiment,in which the first conductivity type is n-type, the n-type dopant ispresent in a concentration ranging from 1×10¹⁴ atoms/cm³ to 1×10¹⁹atoms/cm³.

The dopant concentration that provides the first conductivity type maybe graded or uniform. By “uniform” it is meant that the dopantconcentration is the same throughout the entire thickness of asemiconductor material that provides the crystalline semiconductorsubstrate 110 or the top crystalline semiconductor layer of asemiconductor-on-insulator substrate. For example, a crystallinesemiconductor substrate 110 or the top crystalline semiconductor layerof a semiconductor-on-insulator substrate having a uniform dopantconcentration may have the same dopant concentration at the uppersurface and bottom surface of the semiconductor material that providesthe crystalline semiconductor substrate 110 or the top crystallinesemiconductor layer of a semiconductor-on-insulator substrate, as wellas the same dopant concentration at a central portion of thesemiconductor material between the upper surface and the bottom surfaceof the crystalline semiconductor substrate 110 or the top crystallinesemiconductor layer of a semiconductor-on-insulator substrate. By“graded”, it is meant that the dopant concentration varies throughoutthe thickness of the crystalline semiconductor substrate 110 or the topcrystalline semiconductor layer of a semiconductor-on-insulatorsubstrate. For example, a crystalline semiconductor substrate 110 or thetop crystalline semiconductor layer of a semiconductor-on-insulatorsubstrate having a graded dopant concentration may have an upper surfacewith a greater dopant concentration than the bottom surface of thecrystalline semiconductor substrate 110 or the top crystallinesemiconductor layer of a semiconductor-on-insulator substrate, and viceversa.

The first conductivity type can be introduced during the growth of thecrystalline semiconductor material. Alternatively, the firstconductivity type can be introduced into an intrinsic semiconductormaterial by utilizing ion implantation, and/or gas phase doping.

Next, a passivation layer 114 is provided on an exposed surface of thecrystalline semiconductor substrate 110. The exposed surface can be afront side surface, a back side surface or on both a front side surfaceand a back side surface of the crystalline semiconductor substrate 110.In the drawings, the passivation layer 114 is shown on a front sidesurface, e.g., first surface, of the crystalline semiconductor substrate110, while the back side surface, e.g., second surface which is oppositeto the first surface, is bare. In some embodiments, the back sidesurface of the crystalline semiconductor substrate 110 can be processedto include other components of the bipolar junction transistor, e.g., abase contact and its associated electrode already formed thereon.

Notwithstanding the location of the passivation layer 114, thepassivation layer 114 serves as a passivation layer to saturate danglingbonds on the surface of the crystalline semiconductor substrate 110, inorder to reduce the recombination of carriers at the surface of thecrystalline semiconductor substrate 110. The passivation layer 114 mayalso reduce the recombination of carriers at the surface of thecrystalline semiconductor substrate 110 by “field-induced” passivation,for example, by repelling the minority carriers from the surface of thecrystalline semiconductor substrate 110. Field-induced passivation maybe facilitated by the presence of fixed electronic charges in thepassivation layer, formation of dipoles at the passivation/substrateinterface, or the electric field induced by the work function differencebetween the passivation layer and the substrate semiconductor material.The passivation layer 114 may also serve to prevent air or moisture frombeing introduced into the crystalline semiconductor substrate 110. Thepassivation layer 114 that can be employed in the present inventionincludes, for example, a hard mask material such as, for example, asemiconductor oxide, a semiconductor nitride, a semiconductoroxynitride, or a multilayered stack thereof. The passivation layer 114may also be comprised of a high-k dielectric (k>silicon oxide) such asaluminum oxide or hafnium oxide. In some embodiments, more typical toIII-V materials, the passivation layer 114 may be comprised of asubstantially undoped semiconductor material having a larger bandgapthan that of the crystalline semiconductor substrate 110 to passivatethe surface of the crystalline semiconductor substrate 110 by repellingthe minority carriers induced by the work function difference betweenthe semiconductor materials formed by the passivation layer 114 and thecrystalline semiconductor substrate 110. In other embodiments, thepassivation layer 114 is comprised of silicon oxide, silicon nitride,and/or silicon oxynitride. The passivation layer 114 can have athickness from 5 nm to 50 nm. Other thicknesses that are below or abovethe aforementioned thickness range can also be employed.

In one embodiment, the passivation layer 114 can be formed by adeposition process including, for example, chemical vapor deposition,plasma enhanced chemical vapor deposition, atomic layer deposition orchemical solution. In other embodiments, the passivation layer 114 canbe formed utilizing a thermal technique such as, for example, oxidationand/or nitridation. In yet other embodiments, a combination of adeposition process and a thermal technique can be used to form thepassivation layer 114. In still another embodiment, which is moretypical to III-V materials, a substantially undoped semiconductormaterial having a larger bandgap than that of the crystallinesemiconductor substrate 110 can be used as the passivation layer andsuch a material can be grown on the crystalline semiconductor substrate110 by conventional growth techniques such as, for example, molecularbeam epitaxy or metal-organic chemical vapor deposition. The passivationlayer 114 that is formed at this stage of the present invention is acontiguous blanket layer.

FIG. 2 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 1, after forming at least one opening116 within the passivation layer 114 that exposes at least one portionof the surface of the crystalline semiconductor substrate 110, inaccordance with an embodiment of the present invention. The at least oneopening 116 that can be formed into the passivation layer 114 may be anemitter contact opening, a collector contact opening, a base contactopening, or any combination thereof. In some embodiments, the width ofeach of that contact openings is in the range of 10 nm to 100 nm. Inother embodiments, the width of each of the contact openings is in therange of 50 nm to 100 μm. In yet other embodiments, the width of thecontact openings is in the range of 500 nm to 100 μm. Contact openingsnarrower than 10 nm or wider than 100 μm can also be employed.

The at least one opening 116 that is formed into the passivation layer114 can be formed by lithography followed by etching. In an embodiment,the openings 116 have a smallest dimension F defined by the lithographystep. Lithography includes forming a photoresist material (not shown) onan exposed surface of the passivation layer 114, exposing thephotoresist material to a desired pattern of radiation and developingthe photoresist material utilizing a conventional resist developer. Theetching step, which transfers the pattern from the patterned photoresistinto the passivation layer 114, is preferably dry etching for smallfeatures (i.e., reactive ion etching, ion beam etching, or plasmaetching), and may include wet chemical etching, or a combinationthereof. Typically, a reactive ion etch is used to transfer the patternfrom the patterned photoresist into the passivation layer 114. Afterpattern transfer, the patterned photoresist is typically removed fromthe structure utilizing conventional stripping process such as, forexample, ashing.

FIG. 3 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 2 after growth of a n-type dopant layer118 in the at least one opening 116 from the exposed portion of thesurface of the crystalline semiconductor substrate 110, in accordancewith an embodiment of the present invention. An n-type dopant layer 118,described previously, is epitaxially grown in the at least one opening116 from the exposed portion of the surface of the crystallinesemiconductor substrate 110, after cleaning steps are applied to saidsurface. Epitaxially forming the n-type dopant layer 118 involves usinga process such as molecular beam epitaxy (MBE), metal organic chemicalvapor deposition (MOCVD), atomic layer deposition (ALD), or any othertechnique for epitaxially growing a layer of semiconductor material. Then-type dopant layer 118 is formed to a height lower than the height ofthe passivation layer 114. The n-type dopant layer 118 may have a dopantconcentration in the range from 5×10¹⁸/cm³ to 5×10²⁰/cm³ within theinvention and a good working range is 5×10¹⁹/cm³ to 5×10²⁰/cm³. Thisconcentration is higher than the dopant concentrate in the crystallinesemiconductor substrate 110, discussed previously.

The dopant concentration within dopant layer 118 may be uniform, or mayhave a gradient in concentration referenced to the surface ofcrystalline semiconductor substrate 110. In an embodiment, the leakageat each p/n junction is reduced using a low doped n-type region at theinterface to crystalline semiconductor substrate 110, followed by ahighly doped n-type layer further from the interface (not shown).

FIG. 4 is a pictorial representation (through a cross-sectional view)depicting depositing of a high-k dielectric material 120 over thestructure of FIG. 3, in accordance with an embodiment of the presentinvention. A high-k dielectric material is a material with a highdielectric constant k, for example hafnium oxide (HfO₂). The high-kdielectric material 120 is conformally deposited on the surface of then-type dopant layer 118, and the exposed top and sidewall surface of thepassivation layer 114, preferably using an atomic layer deposition (ALD)process because ALD has the conformality required. In alternativeembodiments, the high-k dielectric material may be comprised of aluminumoxide, titanium oxide, or silicon nitride, and is preferably depositedusing an atomic layer deposition (ALD) process. Any metal oxide that isconformal and resistant to a silicon oxide etch may be used within theinvention. In an alternative embodiment, a thin layer of N±α-SiH (notshown) may be deposited on the n-type dopant layer 118 first to improvetransistor gain and then the high-k dielectric material 120 is depositedon top of the thin layer of N±α-SiH (not shown). The hydrogenatednon-crystalline silicon containing material may include one or more ofthe following elements: Germanium, Carbon, Flourine, Chlorine, Nitrogen,Oxygen, or Deutrerium

FIG. 5 is a pictorial representation of (through a cross-sectional view)depicting the structure of FIG. 4 after chemical-mechanicalplanarization to the height of the passivation layer 114, in accordancewith an embodiment of the present invention. The chemical-mechanicalplanarization removes the high-k dielectric material 120 that is locatedanywhere above the top of the passivation layer 114. Chemical-mechanicalplanarization (CMP) may be used to reduce the height variations in thetopography of deposited high-k dielectric material 120, however,variations may still be present. CMP may use a combination of chemicaletching and mechanical polishing to smooth the surface and even out anyirregular topography. In a preferred embodiment, the height of the topsurface of the high-k dielectric material 120 will be coplanar to theheight of the top surface of the passivation layer 114, as shown in FIG.5.

FIG. 6 is a pictorial representation of (through a cross-sectional view)depicting the structure of FIG. 5 after etching the passivation layer114 between the n-type dopant layer 118 that exposes at least oneportion of the surface of the crystalline semiconductor substrate 110,in accordance with an embodiment of the present invention. The etchingperformed is similar to the etching described above in FIG. 2. Theetching process creates an opening 122 that is formed from the exposedportion of the surface of the crystalline semiconductor substrate 110,the exposed sidewalls of the n-type dopant layer 118, and the exposedsidewalls of the high-k dielectric material 120. In an embodiment, theopening 122 has a smallest dimension (F) defined by the lithographystep.

FIG. 7 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 6 with formed spacers 124, in accordancewith an embodiment of the present invention. Forming dielectric spacers124 may include depositing a conformal layer (not shown) of insulatingmaterial, such as silicon nitride, over crystalline semiconductorsubstrate 110, n-type dopant layer 118, and high-k dielectric material120, such that the thickness of the deposited layer (not shown) on thesidewall of the n-type dopant layer 118 and high-k dielectric material120 is substantially the same as the thickness of the deposited layer(not shown) on the surface of crystalline semiconductor substrate 110.An anisotropic etch process, where the etch rate in the downwarddirection is greater than the etch rate in the lateral direction, may beused to remove portions of the insulating layer, thereby formingdielectric spacer 124. In an embodiment, the opening 122 now has adimension on the surface of 110 that is smaller than defined by thelithography step, specifically this dimension is called w, the basewidth and w=F−2*s, where F is the feature size applied in thelithography step, and s is the sidewall thickness of the dielectricspacer, as covered in detail below.

FIG. 8 is a pictorial representation (through a cross-sectional view)depicting the structure of FIG. 7 after growth of a p-type dopant layer126 between the n-type dopant layer 118 and the formed spacer 124 fromthe exposed at least one portion of the surface of the crystallinesemiconductor substrate 110, in accordance with an embodiment of thepresent invention. A p-type dopant layer 126, describe previously, isepitaxially grown in the opening 122 from the exposed portion of thesurface of the crystalline semiconductor substrate 110. Epitaxiallyforming the p-type dopant layer 126 involves using a process such asmolecular beach epitaxy (MBE), metal organic chemical vapor deposition(MOCVD), thermal chemical vapor deposition, plasma enhanced chemicalvapor deposition (PECVD), liquid phase epitaxy, atomic layer deposition(ALD), or any other technique for epitaxially growing a layer ofsemiconductor material. The p-type dopant layer 126 may have a dopantconcentration in the range from 5×10¹⁸/cm³ to 5×10²⁰/cm³ within theinvention and a good working range is 5×10¹⁹/cm³ to 5×10²⁰/cm³. Thisconcentration is higher than the dopant concentrate in the crystallinesemiconductor substrate 110, discussed previously. The dopantconcentration within p-type dopant layer 126 may be uniform, or may havea gradient in concentration referenced to the surface of crystallinesemiconductor substrate 110. In an embodiment, the leakage at each p/njunction is reduced using a low doped p-type region at the interface tocrystalline semiconductor substrate 110, followed by a highly dopedp-type layer further from the interface (not shown).

As shown in FIG. 8, the base width, w, of the p-type dopant layer isformed at sub-lithographic dimensions. The lithographic feature size orsmallest dimension printed is represented by F. Unique to thisinvention, the base width is measurably smaller than F and is determinedby the formula, w=F−2*s. The dielectric spacer width is s. Uponcompletion of the above described selective method of forming thebipolar junction transistor, electrical wiring contacts are formed toeach base, emitter and collector, and then other devices and componentsmay be formed on crystalline semiconductor substrate 110 andinterconnected using one or more wiring layers. The formation of lowresistance contacts and patterned wiring layers follows methods known inthe art.

Reference is now made to FIGS. 9-15, which illustrate a selective methodof forming a bipolar junction transistor in accordance with anembodiment of the present invention. In the selective method, apatterned high-k dielectric material 214 is formed on an exposed surfaceof a crystalline semiconductor substrate 210. Next, an n-type dopantlayer 218 is epitaxially grown from the exposed surfaces of thecrystalline semiconductor substrate 210. A thermal oxide layer 220 isthen created using thermal oxidation and diffusion 221 of the n-typedopant layer 218 occurs in the crystalline semiconductor substrate 210.The high-k dielectric material 214 between the n-type dopant layers 218is etched to expose at least one portion of the surface of thecrystalline semiconductor substrate 210. A dielectric spacer 224 isformed adjacent to the n-type dopant layer 218 in the exposed area. Ap-type dopant layer 226 is epitaxially grown from the exposed surface ofthe crystalline semiconductor substrate 210.

Referring to FIG. 9, there is a pictorial representation (through across-sectional view) depicting a structure including a high-kdielectric material 214 located atop a crystalline semiconductorsubstrate 210, in accordance with an embodiment of the presentinvention. Crystalline semiconductor substrate 210 is similar tocrystalline semiconductor substrate 110, discussed previously. High-kdielectric material 214 is similar to high-k dielectric material 120,discussed previously.

Referring to FIG. 10, there is a pictorial representation (through across-sectional view) depicting the structure of FIG. 9, after formingat least one opening 216 within the high-k dielectric material 214 thatexposes at least one portion of the surface of the crystallinesemiconductor substrate 210, in accordance with an embodiment of thepresent invention. The forming of at least one opening 216 is similar tothe formation of the at least one opening 116, discussed previously.

Referring to FIG. 11, there is a pictorial representation (through-across-sectional view) depicting the structure of FIG. 10 after growth ofa n-type dopant layer 218 in the at least one opening 216 from theexposed portion of the surface of the crystalline semiconductorsubstrate 210, in accordance with an embodiment of the presentinvention. The n-type dopant layer 218 is similar to the n-type dopantlayer 118, described previously, and is epitaxially grown in a similarfashion. The n-type dopant layer 218 may be formed to a height lower orhigher than the height of the high-k dielectric material 214.

Referring to FIG. 12, there is a pictorial representation (through across-sectional view) depicting the structure of FIG. 11, after thermaloxidation of the exposed n-type dopant layer 218 including diffusion 221into the crystalline semiconductor substrate 210, in accordance with anembodiment of the present invention. Thermal oxidation is used toproduce a thin layer of oxide 220 on the surface of the n-type dopantlayer 218. The technique forces an oxidizing agent to create dopantdiffusion 221 into the crystalline semiconductor substrate 210 at hightemperature. A method of forming the thin layer of oxide 220 by thermaloxidation may be a “dry oxidation” method of thermal oxidation in a pureoxygen atmosphere, forming the oxide film by a pyrogenic oxidationmethod—combusting oxygen and hydrogen in a combustion chamber, addingpure water vapor (H₂O) to an atmosphere gas, flowing the same into areaction chamber and causing thermal oxidation—or a “wet oxidation”method.

Referring to FIG. 13, there is a pictorial representation (through across-sectional view) depicting the structure of FIG. 12 after etchingthe high-k dielectric material 214 between the n-type dopant layers 218that exposes at least one portion of the surface of the crystallinesemiconductor substrate 210, in accordance with an embodiment of thepresent invention. The etching performs a function similar to theetching described above in FIG. 2 and FIG. 6, but the removed dielectricis different from FIG. 2 and FIG. 6. The etching process creates anopening 222 that is formed from the exposed portion of the surface ofthe crystalline semiconductor substrate 210, the exposed sidewalls ofthe n-type dopant layer 218, and the exposed sidewalls of the thin layerof oxide 220. In an embodiment, the opening 222 has a dimension largerthan the base width, w, and optionally this dimension is equal to thelithographic feature size, F.

Referring to FIG. 14, there is a pictorial representation (through across-sectional view) depicting the structure of FIG. 13 with formedspacers 224, in accordance with an embodiment of the present invention.Formation of the spacers 224 is similar to the formation of dielectricspacers 124, discussed previously. The dielectric spacers 224 mayinclude depositing a conformal layer (not shown) of insulating material,such as silicon nitride, silicon oxide, or silicon oxynitride, aluminumoxide, or hafnium oxide over the crystalline semiconductor substrate210, the n-type dopant layer 218, and the thin layer of oxide 220. In anembodiment, an ALD process is used to deposit the spacers 224.

Referring to FIG. 15, there is a pictorial representation (through across-sectional view) depicting the structure of FIG. 14 after growth ofa p-type dopant layer 226 between the n-type dopant layer 218 and formedspacer 224 from the exposed at least one portion of the surface of thecrystalline semiconductor substrate 210, in accordance with anembodiment of the present invention. Formation of a p-type dopant layer226 is similar to the formation of p-type dopant layer 126, discussedpreviously. A thin layer of p-type dopant layer (not shown) is grownfirst to avoid direct contact between the n-type dopant layer 226 andthe diffusion 221. In an alternative embodiment, a thin layer of N±α-SiH(not shown) may be deposited to improve transistor gain.

As shown in FIG. 15, the base width, w, of the p-type dopant layer isformed at sub-lithographic dimensions. The lithographic feature size orsmallest dimension printed is represented by F. Unique to thisinvention, the base width is measurably smaller than F and is determinedby the formula, w=F−2*s. The dielectric spacer width is s. Uponcompletion of the above described selective method of forming thebipolar junction transistor, electrical wiring contacts are formed toeach base, emitter and collector, and then other devices and componentsmay be formed on crystalline semiconductor substrate 210 andinterconnected using one or more wiring layers. The formation of lowresistance contact and patterned wiring layers follows methods known inthe art.

Reference is now made to FIGS. 16-25, which illustrate a selectivemethod of forming a bipolar junction transistor of the presentinvention. In the selective method, a patterned high-k dielectricmaterial or passivation layer 314 is formed on an exposed surface of acrystalline semiconductor substrate 310. Next, an n-type dopant layer318 is epitaxially grown from the exposed surfaces of the crystallinesemiconductor substrate 310. Next, the high-k dielectric material orpassivation layer 314 is etched adjacent the n-type dopant layers 318 toform at least one opening 319 to expose the surface of the crystallinesemiconductor substrate 310. A thin oxide layer 320 is then createdusing thermal oxidation and diffusion 321 of the n-type dopant layers318 occurs in the crystalline semiconductor substrate 310. In anembodiment, next a maskless isotropic time etching is performed toremove the thin oxide layer 320 on the crystalline semiconductorsubstrate 310 but leave the thin oxide layer 320 located on the n-typedopant layers 318. Next a high-k dielectric material 328 is deposited onboth the crystalline semiconductor substrate 310 and the thin oxidelayer 320. Alternatively, a masked isotropic time-etch can be performedto remove the thin oxide layer 320 that exposes at least one portion ofthe surface of the crystalline semiconductor substrate 310. Finally, ap-type dopant layer 326 is epitaxially grown between the n-type dopantlayer and oxide layer from the exposed surface of the crystallinesemiconductor substrate 310.

Referring to FIG. 16, there is a pictorial representation (through across-sectional view) depicting a structure including a high-kdielectric material or passivation layer 314 located atop a crystallinesemiconductor substrate 310, in accordance with an embodiment of thepresent invention. Crystalline semiconductor substrate 310 is similar tocrystalline semiconductor substrate 110 and crystalline semiconductorsubstrate 210, discussed previously. High-k dielectric material orpassivation layer 314 is similar to high-k dielectric material 214 andpassivation layer 114, discussed previously.

Referring now to FIG. 17, there is a pictorial representation (through across-sectional view) depicting the structure of FIG. 16, after formingat least one opening 316 within the high-k dielectric material orpassivation layer 314 that exposes at least one portion of the surfaceof the crystalline semiconductor substrate 310, in accordance with anembodiment of the present invention. The forming of at least one opening316 is similar to the formation of the at least one opening 116 and theat least one opening 216, discussed previously.

Referring now to FIG. 18, there is a pictorial representation (through across-sectional view) depicting the structure of FIG. 17 after growth ofa n-type dopant layer 318 in the at least one opening 316 from theexposed portion of the surface of the crystalline semiconductorsubstrate 310, in accordance with an embodiment of the presentinvention. The n-type dopant layer 318 is similar to the n-type dopantlayer 118 and the n-type dopant layer 218, described previously, and isepitaxially grown in a similar fashion. The n-type dopant layer 218 maybe formed to a height lower or higher than the height of the high-kdielectric material or passivation layer 314.

Referring now to FIG. 19, there is a pictorial representation (through across-sectional view) depicting the structure of FIG. 18 after etchingthe high-k dielectric material or passivation layer 314 adjacent then-type dopant layer 318 to form at least one opening 319 that exposes atleast one portion of the surface of the crystalline semiconductorsubstrate 310, in accordance with an embodiment of the presentinvention. The forming of at least one opening 319 is similar to theformation of the at least one opening 116, the at least one opening 216,and the at least one opening 316, discussed previously.

Referring now to FIG. 20, there is a pictorial representation (through across-sectional view) depicting the structure of FIG. 19 after thermaloxidation of the exposed n-type dopant layer 318 and crystallinesemiconductor substrate 310 including diffusion 321 into the crystallinesemiconductor substrate 310, in accordance with an embodiment of thepresent invention. A thin layer of oxide 320 is formed on the surface ofthe n-type dopant layer 318 and the crystalline semiconductor substrate310 in a similar manner as the previously discussed thin layer of oxide220. The technique forces an oxidizing agent to create dopant diffusion321 similar to dopant diffusion 221 into the crystalline semiconductorsubstrate 310 at high temperature. In an embodiment, the thin layer ofoxide 320 is up to 30% thicker on the n-type dopant layer 318 than thecrystalline semiconductor substrate 310.

Referring now to FIG. 21, there is a pictorial representation (through across-sectional view) depicting the structure of FIG. 20 after masklessisotropic time etching to remove oxide on the crystalline semiconductorsubstrate 310 but leave oxide on the n-type dopant layer 318. Theetching performs a function similar to the etching described above inFIG. 2, FIG. 6, and FIG. 13 but the removed dielectric is different fromFIG. 2 and FIG. 6. The etching process allows the thin layer of oxide320 to remain on the exposed top wall and sidewalls of the n-type dopantlayer 318 and a section of the crystalline semiconductor substrate 310adjacent the n-type dopant layer 318.

Referring now to FIG. 22, there is a pictorial representation (through across-sectional view) depicting depositing of a high-k dielectricmaterial 328 over the structure of FIG. 21, in accordance with anembodiment of the present invention. The high-k dielectric material 328is similar to high-k dielectric material 120, discussed previously, andis deposited in a similar manner as high-k dielectric material 120,discussed previously. The high-k dielectric material 328 extends acrossthe surface of the thin layer of oxide 320.

Referring now to FIG. 23, there is a pictorial representation (through across-sectional view), depicting the structure of FIG. 22 after etchinga portion of the high-k dielectric material 328 on the n-type dopantlayers 318 exposing a portion of the thin layer of oxide 320 on eachn-type dopant layer 318 and etching the high-k dielectric material 328between the n-type dopant layers 318 exposing the surface of thecrystalline semiconductor substrate 310. The etching performed issimilar to the etching described above in FIG. 2, FIG. 6, FIG. 13 andFIG. 21 but the moved dielectric is different than FIG. 2, FIG. 6, andFIG. 21. The etching process allows a portion of the high-k dielectricmaterial 328 to remain on the thin layer of oxide 320 while exposing aportion of the thin layer of oxide 320. Additionally, the etchingprocess exposes the crystalline semiconductor substrate 310 between then-type dopant layers 318. In an embodiment, the opening 322, similar toopening 222 discussed previously, has a dimension larger than the basewidth, w, and optionally this dimension is equal to the lithographicfeature size F.

Referring now to FIG. 24, there is a pictorial representation (through across-sectional view) depicting the structure of FIG. 20 after maskedisotropic time-etch to remove part of the thin layer of oxide 320between the n-type dopant layer 318 that exposes at least one portion ofthe surface of the crystalline semiconductor substrate, in accordancewith an embodiment of the present invention. The etching performed issimilar to the etching described above in FIG. 2, FIG. 6, FIG. 13, andFIG. 21 but the removed dielectric is different from FIG. 2 and FIG. 6.The etching removes part of the thin layer of oxide 320 located on topof the n-type dopant layers and removes the thin layer of oxide 320located on the crystalline semiconductor substrate 310 between then-type dopant layers 318 while leaving the thin layer of oxide 320 onthe side walls of the n-type dopant layers. In an embodiment, theopening 322, similar to opening 222 discussed previously, has adimension larger than the base width, w, and optionally this dimensionis equal to the lithographic feature size F.

Referring now to FIG. 25, there is a pictorial representation (through across-section view) depicting the structure of FIG. 24 after growth of ap-type dopant layer 326 between the n-type dopant layer 318 and the thinlayer of oxide 320 from the exposed at least one portion of the surfaceof the crystalline semiconductor substrate 310, in accordance with anembodiment of the present invention. Formation of the p-type dopantlayer 326 is similar to the formation of p-type dopant layer 126 andp-type dopant layer 226. In an alternative embodiment, the growth of thep-type dopant layer 326 can occur between the n-type dopant layer 318and the thin layer of oxide 320 from the exposed at least one portion ofthe surface of the crystalline semiconductor substrate of the structuredepicted in FIG. 22.

As shown in FIG. 25, the base width, w, of the p-type dopant layer isformed at sub-lithographic dimensions. The lithographic feature size orsmallest dimension printed is represented by F. Unique to thisinvention, the base width is measurably smaller than F and is determinedby the formula, w=F−2*s. The dielectric spacer width is s. Uponcompletion of the above described selective method of forming thebipolar junction transistor, electrical wiring contacts are formed toeach base, emitter and collector, and then other devices and componentsmay be formed on crystalline semiconductor substrate 310 andinterconnected using one or more wiring layers. The formation of lowresistance contacts and patterned wiring layers follows methods known inthe art.

The method as described above is used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

What is claimed is:
 1. A method of forming a bipolar junctiontransistor, the method comprising the steps of: providing asemiconductor layer on an insulating material, wherein the semiconductorlayer forms a base region; depositing a passivation layer on the baseregion; etching two or more openings in the passivation layer, whereinthe two or more openings have a width of a lithographic feature size andexpose the base region; and epitaxially growing a first doped layer inthe two or more openings in the passivation layer, wherein the firstdoped layer is a first doping type.
 2. The method of claim 1, whereinthe insulating material is a buried insulator disposed on thesemiconductor layer.
 3. The method of claim 1, wherein the semiconductorlayer is one of the following: deposited on the insulating material orgrown on to the insulating material.
 4. The method of claim 1, whereinthe passivation layer is one or more of the following: a semiconductoroxide, a semiconductor nitride, a semiconductor oxynitride, a high-kdielectric material, aluminum oxide, hafnium oxide, an undopedsemiconductor material, silicon oxide, silicon nitride, or siliconoxynitride.
 5. The method of claim 1, wherein the passivation layer isbetween 5 nm and 50 nm thick.
 6. The method of claim 1, furthercomprising: conformally depositing a high-k dielectric material on thepassivation layer, a top surface of the first doped layer, and asidewall surface of the passivation layer; planarizing of the high-kdielectric material to a height of the passivation layer, wherein thehigh-k dielectric material is coplanar to a height of a top surface ofthe passivation layer; etching the passivation layer between the firstdoped layer in the two or more openings in the passivation layer toexpose the base region; forming dielectric spacers over the exposed baseregion, the high-k dielectric material, and the first doped layer; andepitaxially growing a second doped layer from the base region betweenthe dielectric spacers and the first doped layer in the two or moreopenings in the passivation layer, wherein the second doped layer is asecond doping type.
 7. The method of claim 6, further comprising: priorto conformally depositing a high-k dielectric material, conformallydepositing a layer of hydrogenated non-crystalline silicon containingmaterial having the first doping type on the passivation layer.
 8. Themethod of claim 6, wherein the high-k dielectric material is one or moreof the following: a material with a high dielectric constant k, hafniumoxide, aluminum oxide, titanium oxide, silicon oxide.
 9. The method ofclaim 1, further comprising: thermally oxidizing a exposed region of thefirst doped layer, wherein thermal oxidation results in diffusion ofdopants from the first doped layer into the base region and forms a thinlayer of oxide on the exposed region of the first doped layer; etchingthe passivation layer between the first doped layer in the two or moreopenings in the passivation layer to expose the base region; formingdielectric spacers over the exposed base region, the thin layer ofoxide, and the first doped layer; and epitaxially growing a second dopedlayer from the base region between the dielectric spacers and the firstdoped layer in the two or more openings in the passivation layer,wherein the second doped layer is a second doping type.
 10. The methodof claim 1, further comprising: etching the passivation layer to exposethe base region; thermally oxidizing the base region and the first dopedlayer forming an oxide layer, wherein the oxide layer has a firstportion on the base region thinner than a second portion on the firstdoped layer, and wherein thermal oxidation results in diffusion ofdopants from the first doped layer into the base region; exposing thebase region by etching the oxide layer until the first portion of theoxide layer on the base region is completely removed while part of thesecond portion of the oxide layer on the first doped layer remains onthe first doped layer; conformally depositing a high-k dielectricmaterial on the oxide layer, wherein the high-k dielectric material isone or more of the following: hafnium oxide, aluminum oxide, titaniumoxide, silicon nitride, or silicon oxynitride; etching the high-kdielectric material on the oxide layer exposing a portion of the oxidelayer and exposing a surface of the base region between the first dopedlayer; and epitaxially growing a second doped layer from the base regionbetween the oxide layer and the first doped layer in the at least oneopening, wherein the second doped layer is a second doping type.
 11. Themethod of claim 1, further comprising: etching the passivation layer toexpose the base region; thermally oxidizing the base region and thefirst doped layer forming an oxide layer, wherein the oxide layer has afirst portion on the base region thinner than a second portion on thefirst doped layer, and wherein thermal oxidation results in diffusion ofdopants from the first doped layer into the base region; exposing thebase region by etching the oxide layer until the first portion of theoxide layer on the base region is completely removed while the secondportion of the oxide layer on the first doped layer remains on the firstdoped layer, wherein the second portion has at least one level ofthickness on top of the first doped layer; and epitaxially growing asecond doped layer from the base region between the oxide layer and thefirst doped layer in the at least one opening, wherein the second dopedlayer is a second doping type.